Trying for 3 years with no pregnancy and no diagnosis yet calls for a proper fertility workup, not one single test. The usual first round checks both partners, since the cause is male-related about as often as it's female-related.
Next Steps
For you this usually means a hormone panel with
AMH for ovarian reserve,
thyroid and
prolactin, plus a pelvic ultrasound to check your uterus and ovaries. An HSG test checks whether your tubes are open. Your husband should also get a semen analysis, since that step often gets skipped.
Health Tips
Please see a fertility specialist or gynaecologist, who can order this whole panel together and build a plan once the results are in.